Objective To explore the underlying mechanism of electroacupuncture (EA) in relieving morphine withdrawal syndrome in rats. Methods Forty SD rats were randomly divided into normal control group

model group 1

model group 2 and EA group. Morphine withdrawal syndrome model was established by muscular injection of morphine (5 mg/kg on the 1st day

progressively increasing everyday till 100 mg/kg on the 20th day) in the hind limbs. Then

rats of model group 1 were anesthetized (10% chloraldurat) to be killed on the 21st day

and those of model group 2 killed on the 27th day. EA (2/100 Hz

2-4 mA) was applied to bilateral "Zusanli" (ST 36) for 30 min

once a day for 7 days. The rat’s thymus was removed (after anesthesia)

cut into sections (4 μm) and stained with immunohistochemical method for displaying the expression of apoptotic promoters Bax

Fas

Fas Ligand (FasL) as well as anti-apoptotic peptide Bcl-2. Results Compared with normal group

Bcl-2 immunoreaction (IR)-positive cell number of model group 1 and group 2 decreased significantly while Bax

Fas and FasL IR-positive cell number and Bax/Bcl-2 in two model groups increased considerably (P<0.01). In comparison with model group 2

Bcl-2 IR-positive cell number of model group 1 decreased significantly (P<0.05)

Bax

Fas and FasL IR-positive cell number and Bax/Bcl-2 of model group 1 were significantly higher (P<0.01

0.05). After EA

in comparison with model group 2

Fas and FasL IR-positive cell number and Bax/Bcl-2 decreased significantly (P< 0.01

0.05)

and Bcl-2 IR-positive cell number increased markedly in EA group (P<0.05); in comparison with model group 1

Bcl-2 IR-positive cell number increased significantly (P<0.01)

while Bax

Fas and FasL IR-positive cell number and Bax/Bcl-2 decreased evidently in EA group (P<0.01). Conclusion EA at "Zusanli" (ST 36) can inhibit morphine-induced downregulation of Bcl-2 and upregulation of Fas and FasL expression

which may contribute to its effect in resisting thymus apoptosis in morphine withdrawal rats.